I would recommend against sandblasting the shell.
In addition to the admonition above, the aluminum part of the Argosy shell (all if it except the end caps) is probably made of the same Alclad that's used in Airstream trailers. Alclad sheet consists of a high strength alloy with .005 of pure aluminum rolled on the outer surface for corrosion resistance. Sandblasting could easily remove most of that top layer.
Get some Removall stripper and give it a try. The thickness of the paint film makes very little difference to Removall because Removall doesn't dissolve the paint--it attacks the bond between the paint and the underlying surface. When I used it I found that in some cases I could get under the clear coat with a plastic putty knife and then just peel off a sheet of clear coat with my fingers--like it was a plastic bag.
Vintage Trailer Supply has it Napier RemovAll 220 - 1 Gallon
and you may be able to find it elsewhere. I got mine from an architectural preservation supply place in Cincinnati, Ohio but that was back when it was made in Canada and a little more commonly available.